Mybatis实现联表查询并且分页功能

今天同学突然问我这个怎么搞。
然后自己搞了一下发现这个玩意有坑。。就记录一下

0. 表结构

person表

cat表

一个person有多个cat

实体类就这么写

1. 实体类

Person实体类

@Data public class Person implements Serializable { private static final long serialVersionUID = - 70682701290685641L ; private Integer personid ; private String firstname ; private String lastname ; private List < Cat > cats ; }

Cat实体类

@Data public class Cat implements Serializable { private static final long serialVersionUID = - 39783356260765568L ; private Integer id ; private String name ; /** * 猫的历史 */ private String history ; /** * 猫的特征 */ private String features ; /** * 大概的样子 */ private String imgurl ; private Integer personId ; }

2. Mapper配置文件

PersonDao.xml

<? xml version = "1.0" encoding = "UTF-8" ?> <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd"> <mapper namespace = "com.liliya.dao.PersonDao" > <!-- 返回的Person映射Map --> <resultMap type = "com.liliya.entity.Person" id = "PersonMap" > <result property = "personid" column = "PersonId" jdbcType = "INTEGER" /> <result property = "firstname" column = "FirstName" jdbcType = "VARCHAR" /> <result property = "lastname" column = "LastName" jdbcType = "VARCHAR" /> <collection property = "cats" ofType = "Cat" > <result property = "id" column = "id" jdbcType = "INTEGER" /> <result property = "name" column = "name" jdbcType = "VARCHAR" /> <result property = "history" column = "history" jdbcType = "VARCHAR" /> <result property = "features" column = "features" jdbcType = "VARCHAR" /> <result property = "imgurl" column = "imgUrl" jdbcType = "VARCHAR" /> <result property = "personId" column = "person_id" jdbcType = "INTEGER" /> </collection> </resultMap>   <!--查询单个--> <select id = "queryById" resultMap = "PersonMap" > select personid, firstname, lastname, id, name, history, features, imgurl, person_id from mybatis.person p inner join mybatis.cat c on p.PersonId = c.person_id and PersonId= #{PersonId} </select>   </mapper>

上面这个是查询单个人的，但是分页没有这么简单
一开始我以为是这么写的,就简单的加一个limit

<select id = "queryById" resultMap = "PersonMap" > select personid, firstname, lastname, id, name, history, features, imgurl, person_id from mybatis.person p inner join mybatis.cat c on p.PersonId = c.person_id limit #{page},#{step} </select>

然后查出来就是这个吊样。。。很明显嘛，不对我的胃口。。

后面我准备放弃的时候突然想到可以来一个子查询。。。

然后我就写出了这样的sql
,在子查询里面套子查询。。。实现limit分页的效果

select personid , firstname , lastname , id , name , history , features , imgurl , person_id from mybatis . person p left join mybatis . cat c on p . PersonId = c . person_id where PersonId in ( select pp . PersonId from ( select person . PersonId from person limit 2 , 2 ) as pp );

然后sql放到上面就搞好了
跑出来的效果就非常nice

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原文链接：https://blog.csdn.net/zhihu_0/article/details/115142044

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